Electric power steering apparatuses are common, which give a steering assist force to a steering mechanism by driving an electric motor in accordance with the steering torque of a steering wheel steered by a driver.
In the steering mechanism, when the steering wheel is continuously steered left or right from its neutral position and a manipulation amount of the steering wheel reaches its maximum steering angle corresponding to the maximum manipulation amount, the steering wheel reaches its steering limit in which a further steering manipulation cannot be performed because the steering mechanism is brought into contact with a mechanical stopper. Such a state of reaching the steering limit in which the steering mechanism is brought into contact with the mechanical stopper is called end contact.
When a steering wheel is manipulated quickly, i.e., when the steering speed is high, the steering assist force generated at the electric power steering apparatus also increases, meaning that an impact force generated at the time of the end contact also becomes large. This may result in deterioration in durability of the steering mechanism or may give a driver uncomfortable feeling during manipulation of the steering wheel.
Then, Patent Literature 1, for example, describes a technique for an electric power steering apparatus to alleviate the impact at the time of an end contact. In this technique, when the steering wheel approaches a predetermined maximum steering angle and exceeds an attenuation starting steering angle is detected, the driving force of the electric motor is attenuated. In this technique, the attenuation starting steering angle is set in accordance with the load of the steering wheel and the steering speed of the steering wheel.